本來(lái)想看完pagefault的處理的,不過(guò)實(shí)驗(yàn)室有事情了,只能先把這一半放上來(lái)了。
頁(yè)面的分配與回收使用了一個(gè)叫做buddy allocator的機(jī)制,kernelnewbies上的解釋
The memory allocation scheme used in the kernel. A vector of lists of free pages is kept, ordered by the size of the chunk (in powers of two). When a chunk is allocated, it is removed from the relevant list. When a chunk is freed back to the free pages pool, it is placed in the relevant list, starting from the top. If it is physically contiguous with a present chunk, they are merged and placed in the list above (i.e. where the chunks are twice the size), and this operation percolates up the vector. As regions are merged whenever possible, this design helps to reduce memory fragmentation.
首先在zone_struct{} 中保存了一個(gè)free_area_t數(shù)組,這個(gè)數(shù)組記錄了各種大小的空閑內(nèi)存塊的信息。
include/linux/mmzone.h:














































free_area_struct {}








頁(yè)面分配時(shí),找到適合大小的free_area_struct{},然后從free_list中找有沒(méi)有空閑的內(nèi)存塊,如果沒(méi)有就找更大的free_area_struct{},因?yàn)榇笮《际?^n,很容易把大塊內(nèi)存拆開(kāi),一塊分配給請(qǐng)求,剩下的保存到對(duì)應(yīng)大小的隊(duì)列中。
頁(yè)面回收時(shí)主要的問(wèn)題是如何解決過(guò)多的內(nèi)存碎片。當(dāng)頁(yè)面塊被釋放時(shí),先檢查是否有相同大小的相鄰空閑塊存在,如果有的話就結(jié)合起來(lái)(遞歸過(guò)程)。